Acid-Base TitrationsCambridge IGCSE Chemistry: Revision notes
Section 1
What Apparatus Is Used in a Titration?
An acid-base titration is carried out using specific apparatus, each chosen for accurate measurement:
- Burette — used to add one solution (usually the acid or alkali being measured) gradually and accurately, reading the volume delivered
- Volumetric pipette — used to measure out a fixed, precise volume of the other solution into a flask
- Suitable indicator — added to the flask to signal the exact point of neutralisation
Other general apparatus such as balances, measuring cylinders and thermometers may be used elsewhere in experimental chemistry, but the burette and pipette are specific to accurate titration work.
Section 2
What Is the Method for an Acid-Base Titration?
A typical acid-base titration follows these steps:
- Use a volumetric pipette to measure a fixed volume of one solution (e.g. the alkali) into a conical flask
- Add a few drops of a suitable indicator to the flask
- Fill a burette with the other solution (e.g. the acid)
- Add the solution from the burette to the flask slowly, swirling constantly, until the indicator just changes colour
- Record the volume of solution used from the burette
Doing a rough titration first, then repeating with more precision (adding drop by drop near the expected end-point), improves accuracy.
Section 3
How Do You Identify the End-Point?
The end-point of a titration is identified by the colour change of the indicator — this signals that neutralisation has just occurred (or is very close to complete).
Different indicators change colour at different points, so choosing a suitable indicator for the specific acid-alkali combination is important for an accurate result.
With phenolphthalein, the end-point is seen as the solution changes from pink to colourless as acid is added to an alkali.
Section 4
Why Choose These Techniques and Apparatus?
When suggesting or evaluating experimental methods and apparatus, you should be able to discuss their advantages and disadvantages:
- A burette allows a precise, variable volume to be added and measured, which a measuring cylinder cannot do as accurately
- A volumetric pipette measures one fixed volume very precisely, but cannot be adjusted to a different volume
- Indicators are simple and cheap but rely on a visible colour change, which can be harder to judge with coloured solutions
Don't confuse a burette (variable volume, used for the titrant) with a volumetric pipette (one fixed volume, used to measure out the flask solution) — they serve different purposes in a titration.
Must Know
- A titration uses a burette (variable volume, added slowly) and a volumetric pipette (one fixed, precise volume)
- A suitable indicator is added to the flask to detect the end-point
- The end-point is identified by the colour change of the indicator
- Method: pipette one solution into a flask, add indicator, add the other solution from the burette until the colour changes, record the volume used
- Apparatus choice affects accuracy — burettes/pipettes give more precise volumes than measuring cylinders
- Titrations are used to find the volume of one solution that exactly reacts with a known volume of another
That's the notes covered.
Carry on to the next subtopic.